On 03/11, Dan Carpenter wrote:
>
> On Tue, Mar 10, 2020 at 04:07:14PM +0100, Oleg Nesterov wrote:
> > Annoyingly, this triggers a lot of sparse_error's in pre-process.c:collect_arg().
> > And just in case, of course this is not specific to dissect/sindex, ./sparse or
> > anything else will equally complain.
> >
> > For example,
> >
> > 1011 static inline bool page_expected_state(struct page *page,
> > 1012 unsigned long check_flags)
> > 1013 {
> > 1014 if (unlikely(atomic_read(&page->_mapcount) != -1))
> > 1015 return false;
> > 1016
> > 1017 if (unlikely((unsigned long)page->mapping |
> > 1018 page_ref_count(page) |
> > 1019 #ifdef CONFIG_MEMCG
> > 1020 (unsigned long)page->mem_cgroup |
> > 1021 #endif
> > 1022 (page->flags & check_flags)))
> > 1023 return false;
> > 1024
> > 1025 return true;
> > 1026 }
> >
> > leads to
> >
> > mm/page_alloc.c:1019:1: error: directive in macro's argument list
> > mm/page_alloc.c:1021:1: error: directive in macro's argument list
>
> This does:
>
> /* Shut up warnings after an error */
> has_error |= ERROR_CURR_PHASE;
>
> so we probably end up not seeing some warnings.
Heh,
./include/trace/events/neigh.h:127:1: error: directive in macro's argument list
./include/trace/events/neigh.h:199:1: error: too many errors
so we probably end up not seeing some errors ;)
> > and it is not immediately clear why. Yes, because "unlikely" is a macro.
> >
> > Can't we simply remove this sparse_error() ? "#if" inside the macro's args
> > is widely used in kernel, gcc doesn't complain, afaics pre-process.c handles
> > this case correctly.
>
> s/correctly/the same as GCC/. The behavior is undefined in c99.
Yes, yes, this is what I meant.
and just in case... there are other cases when GCC and sparse differ,
if, within a macro invocation, that macro is redefined, then the new
definition takes effect in time for argument pre-expansion, but the
original definition is still used for argument replacement. Here is a
pathological example:
#define f(x) x x
f (1
#undef f
#define f 2
f)
which expands to
1 2 1 2
./sparse -E outputs
/tmp/M.c:3:1: error: directive in macro's argument list
/tmp/M.c:4:1: error: directive in macro's argument list
2
but I think we don't care.
Oleg.
